My invention relates to load-handling gantries of the type having a load-carrying member, such as a bridging I-beam, which is supported at longitudinally spaced stations by pairs of braced and variably divergent legs. The legs and braces are associated with the upper flange of the I-beam, and its lower flange commonly carries a trolley from which a load may be movably suspended and may be raised and lowered by a hoist or the like.
The development of several prior gantries is typified by U.S. Pat. Nos. 2,990,788, 2,995,094, 3,490,385 and 3,826,196, granted, respectively, on July 4, 1961, Aug. 8, 1961, Jan. 20, 1970, and July 30, 1974. These gantries provide features of adjustability, including variation in leg length and divergence; and one patented embodiment, because of the use of a main I-beam in conjunction with a pair of auxiliary I-beam sections, is usable in a variety of configurations including what has become known as inboard, outboard, and combination leg bracing. Also, because of its triple I-beam, this patented construction has afforded adjustability of gantry span, and provision of beam overhang.
In brief, those earlier patented gantries have, individually, various features of adjustability, and utility in various configurations. However this has not been achieved without acceptance of a number of shortcomings, principally in that, to realize the greatest adjustability, it has been necessary to accept a three-part bridging beam structure, and to aperture both the web and flanging to accept movable mounting bolts.
A further shortcoming was the loss of headroom due to the double I-beam used. A still further disadvantage came from the added weight of the extra I-beam members. A further disadvantage was the added cost due to the extra I-beams and related hardware, which sometimes increased the cost of gantries by 20% to 30%.